The present invention concerns time locks and more particularly locks whose operation can be disabled during predetermined time intervals the duration of which can be fixed by one or more timing devices. Such time locks are used principally in protected enclosures such as bank strong rooms and safes to prevent any manual actuation of the door for example during the bank's closing hours.
In this application, the control box of the lock containing notably the timing device and the blocking members of the lock mechanism is preferably mounted on the inside of the door. It is thus desirable, for security reasons, to avoid any electrical connection between the door and the surrounding door frame and for this reason time locks of this type usually include one or more mechanical timing devices able to operate without any source of electricity, i.e. driven solely by means of energy provided by a spring.
Such a mechanical timing device described for example in French patent FR-A-2,435,584 (U.S. Pat. No. 4,269,050) generally comprises a spring-operated adjustable clockwork mechanism whose spring is wound up to a greater or lesser degree to set the variable duration of the count-down time of the timing device.
Members coupled to the spring for the purpose of winding it are generally provided with a dial and an index which display the chosen duration to the user. Once the setting operation has been finished, the spring drives the clockwork mechanism until the selected duration has elapsed.
However, it is possible that the user inadvertently exceeds the duration he wished to select by moving the winding members beyond the position corresponding to the desired duration. It would then be impossible for him to go back unless the winding members or the wheel-train coupling the spring and the regulator include a friction coupling. Apart from encumbering the timing device mechanism, such a coupling does not allow an easy and precise backwards correction to the adjustment and the user would be obliged to resort to trial and error and, to obtain the position corresponding to the desired duration, would have to make several tries.
Furthermore, the blocking members of the lock's linkage system can only be released by supplying a given quantity of energy which must come from the mechanical timing device itself and more specifically from its spring. However, this release necessarily occurs at the end of the movement of the timing device when the spring has already lost most of its stored energy so that there may be problems in overcoming all of the forces necessary to release the lock. Whereas it is possible by calculation to provide a spring with a sufficient residual energy, the precise instant when release is to take place is, to the contrary, uncertain, especially as the timing devices preferably have a maximum adjustable time of 144 hours. Hence, the precision of determining the instant of release is low and may even vary from 30 to 60 minutes if the timing device is set at its maximum period.